Type 1 diabetes mellitus (T1DM) results from the immune- (specifically T cell-) mediated destruction of the body's only cells capable of physiologically regulated insulin secretion, the pancreatic beta cells. Beta cells comprise an estimated 2% of the pancreatic cell number and are grouped together into cell clusters (along with blood vessels and other cells making hormones like glucagon, somatostatin, pancreatic polypeptide) into "mini-organs" called the islets of Langerhans. The islet as "mini-organ" concept is apt for at least 2 reasons: (1) while the cellular organization is different for different species, the various islet cell types are nevertheless organized in a very orchestrated way, and (2) islets consume more pancreatic blood flow (about 20%) than their small mass would suggest. Thus islets are important if incompletely understood structures with unique anatomical, physiological, and immunological features; and they represent an Achilles' heel for individuals destined to develop T1DM. This project has had multiple components, to: (1) characterize isolated islet structure, function, and quality, (2) test, using a non-human primate islet transplant model, important pre-clinical questions, (3) perform human clinical islet transplants using carefully planned protocols, (4) develop clinical assays for characterizing islet function pre- and post-transplant, (5) develop a renewable islet source, (6) test novel ways of preventing islet allograft rejection following transplant, and more recently (7) test systems for imaging pancreatic islets in vivo. Beginning in 7/99, in collaboration with the Clinical Center's Department of Transfusion Medicine/Cell Processing Unit (with much early assistance from the University of Miami's Dr. Camillo Ricordi), islets have been isolated from both human and non-human primate pancreata. Many islets have been shared with various intra- and extra-mural collaborators pursuing shared goals as enumerated above. We established 2 separate isolation laboratories with technicians for both; one for human glands and one for animal pancreata. We have tested new in vitro islet function assays and made, or further pursued, several novel observations including: a) using RNA expression microarray analysis we found that islets express, and in a highly regulated, glucose-responsive way, a TGF-beta gene that appears to play a role in beta cell survival, b) identified an insulin RNA splice form translated into protein more efficiently than the native splice form, and found that this splice form is highly expressed in islet tumors, and c) demonstrated that islets produce the hormone resistin, previously thought to be expressed only in fat. Several intra- and extra- collaborators are attempting various techniques to culture islets in vitro so as to increase islet function and/or number, and Branch investigators have played a leadership role in the international group called the Beta Cell Biology Consortium. In addition, through follow up of non-human primates given an islet transplant, we found a previously unknown mechanism whereby the transplant improves glycemia control; i.e. by inhibiting the over-expression of the hormone glucagon displayed by patients with diabetes. We are now engaged in studies testing whether islet like clusters grown in vitro can re-differentiate in vivo into insulin producing cells capable of physiologically regulated insulin secretion sufficient to maintain normal blood glucose levels in a relevant pre-clinical model. Of course, the most immediately relevant product of our research is the knowledge gained from our clinical islet transplant experience which included 6 patients with long-standing and difficult to control T1DM. Detailed metabolic testing of the patients found they had basically normal insulin sensitivity, but even the insulin independent patients had only marginal islet function and imperfect glycemia control. Due to our belief that the factors limiting islet transplantation (primarily the inadequate donor islet supply, and imperfect immunosuppressive regimens) were not being effectively and most safely addressed by the solitary islet transplant protocol, we suspended patient accrual, but have published several observations from our experience. For instance, this year we published several widely quoted overviews enumerating the problems that must be overcome to make islet transplantation a clinically relevant treatment approach, and this work has been highlighted by a report in Science (Vol 306, pages 34-37, 2004). On a more positive note, we observed that a surprising number with even long-standing and difficult to control T1DM maintain a limited capacity for endogenous insulin production. This observation, inconsistent with the most widely held model for T1DM that has suggested patients lose all insulin producing capacity, has prompted three new protocols designed to test whether under controlled conditions (i.e. controlling both the autoimmune response and the patient?s blood glucose and blood lipids), the pancreas in patients with long standing T1DM might actually recover insulin producing capacity. For instance, we have developed a clinical protocol (currently completing Institutional Review Board review) to assess whether patients long-functioning pancreas allografts display evidence that their native (as opposed to the transplanted) pancreas has resumed making insulin. Also, in conjunction with Drs. John Tisdale, Shira Perl, and Bruce Buchholz (Lawrence Livermore National Laboratory), we are testing the age of human pancreatic beta cells from brain dead organ donors using a novel technique to measure the 14C present in the DNA from those cells. Last, as described in Project Number DK062002-05, we are testing whether combination therapy with insulin (to maintain near normal glycemia control), an experimental agent called Exendin-4, and/or immunosuppression can promote pancreatic islet functional recovery in patients with long-standing T1DM.